1. Field of the Invention
This invention relates to constant velocity coupling for translating the rotary motion of a nutating motor rotor to an output shaft.
2. Background of the Invention
A nutating motor is one which employs a wobbling, or nutating, rotor element. The rotor element is caused to wobble by sequentially energizing appropriate stator windings in the motor. A pair of ring gears having oppositely spaced gear teeth are provided on the wobbling rotor element and on the stator housing. The rotor is made of magnetically permeable material so that the rotating magnetic fields produced by the stator windings cause successive adjacent sectors of the rotor to be pulled toward the successively energized adjacent stator windings and the rotor moves with a wobbling motion about a motor shaft. The rotor element is oftentimes a disc which has an axis extending nomally to its face. As the rotor nutates or wobbles, the axis of the rotor describes a conical figure around the axis of the motor output shaft. Relative rotation occurs between the two engaging ring gears on a rotor and on a stator if the engaging ring gears have a different number of teeth. For each nutational cycle of the rotor, the rotor will rotate with respect to the stator an angular distance determined by the difference between the number of gear teeth.
Various means for coupling a wobbling or nutating rotor element to an output shaft and for supporting the rotor element are known in the prior art. It is desirable that any coupling or universal joint used with a nutating motor be a constant angular velocity type. U.S. Pat. No. 3,428,839 discloses a double-yoke universal joint. U.S. Pat. No. 3,492,515 discloses a modified ball and socket coupling in which the ball is fixed to the output shaft and the nutating rotor element is coupled to a socket which is generally aligned in the direction of the shaft. U.S. Pat. No. 3,530,322 discloses a ball fixed to an output shaft and rotor having a centrally located socket for engaging the ball. These couplings are subject to friction and wear.
Prior art universal couplings for nutating motors also include ball couplings having a plurality of balls spaced equidistantly around the axis of the output shaft. The balls are held in position by means of a retainer ring having holes therein for holding the balls. An outer ball guide includes arcuate ball guide surfaces. A correspondingly matched inner ball guide includes correspondingly matched arcuate slots. This type of coupling member requires precision machining of the arcuate surfaces in addition to requiring a separate ball retaining ring.